[MetaRenamer] Don't rename library functions.

Library functions can have specific semantics that affect the behavior of
certain passes. DSE, for instance, gives special treatment to malloc-ed pointers
but not to pointers returned from an equivalently typed (but differently named)
function.

MetaRenamer ought not to alter program semantics, so library functions must
remain untouched.

Reviewers: mehdi_amini, majnemer, chandlerc, davide

Reviewed By: davide

Subscribers: davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D31304

llvm-svn: 298659

2 files changed, 29 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/MetaRenamer.cpp b/llvm/lib/Transforms/Utils/MetaRenamer.cpp
index c999bd008fe..481c6aa29c3 100644
--- a/llvm/lib/Transforms/Utils/MetaRenamer.cpp
+++ b/llvm/lib/Transforms/Utils/MetaRenamer.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Transforms/IPO.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
@@ -67,6 +68,7 @@ namespace {
     }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<TargetLibraryInfoWrapperPass>();
       AU.setPreservesAll();
     }
 
@@ -110,9 +112,15 @@ namespace {
       }
 
       // Rename all functions
+      const TargetLibraryInfo &TLI =
+          getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
       for (auto &F : M) {
         StringRef Name = F.getName();
-        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
+        LibFunc Tmp;
+        // Leave library functions alone because their presence or absence could
+        // affect the behavior of other passes.
+        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
+            TLI.getLibFunc(F, Tmp))
           continue;
 
         F.setName(renamer.newName());
@@ -139,8 +147,11 @@ namespace {
 }
 
 char MetaRenamer::ID = 0;
-INITIALIZE_PASS(MetaRenamer, "metarenamer", 
-                "Assign new names to everything", false, false)
+INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
+                      "Assign new names to everything", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
+                    "Assign new names to everything", false, false)
 //===----------------------------------------------------------------------===//
 //
 // MetaRenamer - Rename everything with metasyntactic names.
diff --git a/llvm/test/Transforms/MetaRenamer/metarenamer.ll b/llvm/test/Transforms/MetaRenamer/metarenamer.ll
index 213fbe3bbff..7b527ae54cb 100644
--- a/llvm/test/Transforms/MetaRenamer/metarenamer.ll
+++ b/llvm/test/Transforms/MetaRenamer/metarenamer.ll
@@ -96,3 +96,18 @@ define i32 @varargs_func_6_xxx(i32 %arg_1_xxx, i32 %arg_2_xxx, ...) nounwind uwt
   store i32 %arg_2_xxx, i32* %2, align 4
   ret i32 6
 }
+
+declare noalias i8* @malloc(i32)
+declare void @free(i8* nocapture)
+
+define void @dont_rename_lib_funcs() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = call i8* @malloc(i32 23)
+; CHECK-NEXT:    call void @free(i8* [[TMP]])
+; CHECK-NEXT:    ret void
+;
+  %x = call i8* @malloc(i32 23)
+  call void @free(i8* %x)
+  ret void
+}